Over the years general purpose boxcars have progressed from relatively simple wooden structures mounted on flat cars to more elaborate arrangements including insulated walls and refrigeration equipment. Various types of insulated and uninsulated boxcars are presently manufactured and used. A typical boxcar includes an enclosed structure mounted on a railway car underframe. The enclosed structure generally includes a floor assembly, a pair of sidewalls, a pair of endwalls and a roof assembly. Insulated boxcars often include sidewalls, endwalls and a roof formed in part by an outer shell, one or more layers of insulation and an interior surface.
The outer shell of many boxcars may be formed from various types of metal such as steel or aluminum. The interior surfaces may be formed from wood and/or metal as desired for specific applications. For some applications the interior surfaces may be formed from fiber reinforced plastic (FRP). Various types of sliding doors including plug type doors are generally provided on each side of a boxcar for loading and unloading freight.
The underframe for many boxcars includes a center sill with a pair of end sill assemblies and a pair of side sill assemblies arranged in a generally rectangular configuration corresponding approximately with dimensions of the floor assembly of the boxcar. Cross bearers and/or cross ties may be provided to establish desired rigidity and strength for transmission of vertical loads from the floor assembly to associated side sills which in turn transmit the vertical loads from the floor assembly to associated body bolsters and for distributing horizontal end loads on the center sill to other portions of the underframe. Cross bearers and cross ties generally cooperate with each other to support a plurality of longitudinal stringers. The longitudinal stringers are often provided on each side of the center sill to support the floor assembly of a boxcar.
Applicable standards of the Association of American Railroads (AAR) established maximum total weight on rail for any railway car including boxcars, freight cars, hopper cars, gondola cars, and temperature controlled railway cars within prescribed limits of length, width, height, etc. All railway cars operating on commercial rail lines in the U.S. must have exterior dimensions which satisfy associated AAR clearance plates. Therefore, the maximum load which may be carried by any railway car is typically limited by the applicable AAR clearance plate and empty weight of the railway car.
Reducing the empty weight of a railway car or increasing interior dimensions may increase both volumetric capacity and maximum load capacity of a railway car while still meeting applicable AAR standards for total weight on rail and exterior dimensions for applicable AAR clearance plate. Traditionally, insulated boxcars have less inside height and width than desired for cost effective shipment of some types of lading. The maximum exterior width of an insulated boxcar is limited by applicable AAR clearance plates. The maximum interior width is limited by the amount (thickness) of insulation required to satisfy applicable AAR heat transfer limitations or UA factor. Door operating tubes, door bottom tracks and door handles are often built to the extreme width of applicable AAR plate diagrams. Locating door assembly components at the maximum width provides as much interior width as possible for carrying lading within an insulated boxcar or uninsulated boxcar. Door assembly components for many conventional insulated boxcars may extend approximately four inches (4″) from each ride of the boxcar. Therefore, interior dimensions of such boxcars are also limited by the four inch extension of the associated door assemblies.
Conventional insulated boxcars may have an inside width of nine feet or less while many uninsulated boxcars often have an inside width of approximately nine feet, six inches. Prior insulated boxcars have been relatively ineffective at increasing interior volumetric capacity while maintaining desired UA rating or minimum insulation efficiency required by AAR. UA may be generally described as the number of BTU's per hour per degree Fahrenheit which transfer through the roof assembly, sidewall assemblies, endwall assemblies and/or floor assembly of an insulated boxcar.
At least one insulated boxcar has been built with a nominal length of fifty two feet six inches (52′ 6″) and an interior width of approximately nine feet six inches (9′6″). This particular insulated boxcar had a UA factor of 285 BTU/° F./hour which is greater than applicable AAR requirements. AAR specifications place various requirements on insulated boxcars such as sidewalls, endwalls, floor and roof having a maximum UA factor of 250 BTU/° F./hour for a fifty foot boxcar and a maximum UA factor of 300 BTU/° F./hour for a sixty foot boxcar.